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Council hears final drainage master plan; staff recommends adopting preliminary county maps and nine priority projects
Summary
Consultants presented a rapid-assessment drainage master plan that identifies about 741 structures newly within a 1% annual-risk floodplain on preliminary county maps, ranks candidate projects and recommends the city adopt Williamson County's preliminary floodplain maps for development review and pursue funding for priority projects.
Consultants and city staff presented the final Hutto Drainage Master Plan at the April 3 council meeting, saying preliminary county flood mapping and updated rainfall data greatly expanded the city's estimated flood exposure and that a prioritized package of projects and monitoring investments will be needed to reduce risk.
City Engineer Matt Recker and consultant Andy Brook (project lead) summarized the study. Brook said the county's preliminary work and newer precipitation data (Atlas 14) increased Hutto's estimated structures in the 1% annual chance floodplain from about 71 to roughly 741 within city limits. "A 100-year flood plain doesn't occur once every 100 years; it has a 1% chance of occurring in any given year," Brook told council. He said the study used rapid-assessment 1D and 2D modeling to identify pockets of concentrated risk and produced a ranked list of 13 candidate projects (later reduced to nine recommended projects) including channel widening, detention repairs and a city-wide gauging and warning system.
Why it matters: Staff said the change in mapping and rainfall statistics means many more properties could be designated flood-prone when FEMA finalizes updated maps, which can trigger insurance requirements and development constraints. The plan recommends early adoption of the Williamson County preliminary maps for development review, prioritized design of nine projects (estimated total roughly $149 million, with the most costly projects concentrated on Cottonwood Creek), and improvements to maintenance and monitoring.
Plan details and recommendations: The report evaluated detention pond repair, roadside-ditch-to-storm-drain conversions, channelization, and one large detention facility. Brook and Recker said some projects are high-cost per structure removed and that alternatives such as property buyouts should be considered. The plan also recommends a city-wide monitoring network and a targeted deferred-maintenance program (for example, repairing a damaged outlet structure at Emery Farms) and suggested the city review drainage fees and consider a tiered structure to raise funds for operations and maintenance.
Council response and next steps: Staff told council that a consent agenda item to accept the plan was placed on the meeting agenda; the consent agenda passed. Consultants and staff recommended formally adopting the county's preliminary floodplain mapping for planning and development reviews to avoid permitting new construction into areas likely to be remapped. Council members asked questions about timing, funding and how the city would engage property owners; staff suggested pursuing Texas Water Development Board and other state funding programs and recommended starting project-level design on the highest-ranked items when funding is available.
What to watch: The county's maps must still complete FEMA's review process; staff said the county meeting and FEMA procedures could make the maps effective through late next year. The master plan identifies near-term maintenance and monitoring actions staff can begin while pursuing funding for large capital projects.
